Proxy support

[rubikonx9]

I'm behind corporate proxy. I don't use any Proxy Authentication.

Attempt to download either audio or video results in an error being displayed:

ERROR: Unable to download webpage: <urlopen error Tunnel connection failed: 407 Proxy Authentication Required> (caused by URLError(OSError('Tunnel connection failed: 407 Proxy Authentication Required')))

The youtube itself - via web browser - works just fine.

--EDIT I was able to make it work by adding the arguments to youtube-dl call: "--proxy", "socks5://<my_proxy_address>:<my_proxy_port>/" in the extension.js file.

So the issue is actually about adding a configuration option.